S. Van Vlierberghe

Biopolymer-Based Hydrogels As Scaffolds for Tissue Engineering Applications: A Review

Hydrogels are physically or chemically cross-linked polymer networks that are able to absorb large amounts of water. They can be classified into different categories depending on various parameters including the preparation method, the charge, and the mechanical and structural characteristics. The present review aims to give an overview of hydrogels based on natural polymers and their various applications in the field of tissue engineering. In a first part, relevant parameters describing different hydrogel properties and the strategies applied to finetune these characteristics will be described. In a second part, an important class of biopolymers that possess thermosensitive properties (UCST or LCST behavior) will be discussed. Another part of the review will be devoted to the application of cryogels. Finally, the most relevant biopolymer-based hydrogel systems, the different methods of preparation, as well as an in depth overview of the applications in the field of tissue engineering will be given.

Correlation Between Cryogenic Parameters and Physico-Chemical Properties of Porous Gelatin Cryogels

In the present work, we have performed an in-depth physico-chemical and bio-physical evaluation of a series of previously described porous gelatin scaffolds (S. VanVlierberghe, V. Cnudde, P. Dubruel, B. Masschaele, A. Cosijns, I. DePaepe, P.J.S. Jacobs, L. VanHoorebeke, J.P. Remon and E. Schacht, Biomacromolecules 8, 331 (2007)). All scaffolds were prepared by a cryogenic treatment and subsequent freeze-drying. Three types of scaffolds were prepared by using different gelatin concentrations and cooling protocols. Type-I hydrogels were composed of cone-like pores with decreasing diameter from top (330 μm) to bottom (20–30 μm). Type-II and type-III scaffolds contained spherical pores with an average diameter of 135 (type II) and 65 μm (type III), respectively. The physico-chemical and bio-physical properties studied include the water uptake capacity and kinetics, the mechanical properties and the enzyme-mediated degradation. We can conclude that the pore geometry affects the water uptake capacity, the mechanical properties and the degradation profile of the hydrogels. Type-I hydrogels possess the highest water uptake, the lowest compression modulus and the fastest enzyme mediated degradation, indicating a clear effect of the pore morphology (elongated channels for type I versus spherical pores for types II and III) on the physico-chemical and bio-physical properties of the materials. In contrast to the effect of the pore geometry (channel-like versus spherical), the pore size does not significantly affect the water uptake, the mechanical properties and the enzyme mediated degradation in the investigated pore size range (65–135 μm). To the best of our knowledge, this is the first report in which the effects of a cryogenic treatment on the hydrogel network properties are investigated in such detail.

Effects of electromagnetic stimulation on osteogenic differentiation of human mesenchymal stromal cells seeded onto gelatin cryogel.

Bone tissue engineering typically uses biomaterial scaffolds, osteoblasts or cells that can become osteoblasts, and biophysical stimulations to promote cell attachment and differentiation. In this study, we investigated the effects of an electromagnetic wave on mesenchymal stromal cells isolated from the bone marrow and seeded upon gelatin cryogel disks. In comparison with control conditions without electromagnetic stimulus, the electromagnetic treatment (magnetic field, 2 mT; frequency, 75 Hz) increased the cell proliferation and differentiation and enhanced the biomaterial surface coating with bone extracellular matrix proteins. Using this tissue-engineering approach, the gelatin biomaterial, coated with differentiated cells and their extracellular matrix proteins, may be used in clinical applications as an implant for bone defect repair.

Surface Modification of Polyimide Sheets for Regenerative Medicine Applications

In the present work, two strategies were elaborated to surface-functionalize implantable polyimide sheets. In the first methodology, cross-linkable vinyl groups were introduced on the polyimide surface using aminopropylmethacrylamide. In the second approach, a reactive succinimidyl ester was introduced on the surface of PI. Using the former approach, the aim is to apply a vinyl functionalized biopolymer coating. In the latter approach, any amine containing biopolymer can be immobilized. The foils developed were characterized in depth using a variety of characterization techniques including atomic force microscopy, static contact angle measurements, and X-ray photoelectron spectroscopy. The results indicated that both modification strategies were successful. The subcutaneous implantation in mice indicated that both modification strategies resulted in biocompatible materials, inducing only limited cellular infiltration to the surrounding tissue.

Effect of cryogenic treatment on the rheological properties of gelatin hydrogels

Gelatin has the ability to form a gel when cooled below the sol—gel temperature. In this study, the effects of various cryo-parameters, including the number of freeze—thaw cycles, cooling rate, thawing rate, and gelatin concentration, on the material properties were examined. The rheological properties of the cryogels improved with increasing cryo-cycles and decreasing cooling and thawing rates as well as were superior to those of the corresponding hydrogels formed at room temperature. In addition, the critical gelation concentration decreased after repeated cryo-treatments. Methacrylamide-modified gelatin was also treated cryogenically, followed by in situ UV irradiation to enable radical cross-linking. The cross-linking efficiency of specific gelatin concentrations improved with freeze—thawing. Cryogelation can be used to fine-tune the mechanical properties of hydrogels. This is of relevance to tissue engineering where porous gelatin hydrogels are used as biomaterials.

Soft tissue fillers for adipose tissue regeneration : from hydrogel development toward clinical applications

There is a clear and urgent clinical need to develop soft tissue fillers that outperform the materials currently used for adipose tissue reconstruction. Recently, extensive research has been performed within this field of adipose tissue engineering as the commercially available products and the currently existing techniques are concomitant with several disadvantages. Commercial products are highly expensive and associated with an imposing need for repeated injections. Lipofilling or free fat transfer has an unpredictable outcome with respect to cell survival and potential resorption of the fat grafts. Therefore, researchers are predominantly investigating two challenging adipose tissue engineering strategies: in situ injectable materials and porous 3D printed scaffolds. The present work provides an overview of current research encompassing synthetic, biopolymer-based and extracellular matrix-derived materials with a clear focus on emerging fabrication technologies and developments realized throughout the last decade. Moreover, clinical relevance of the most promising materials will be discussed, together with potential concerns associated with their application in the clinic.

Electromagnetic stimulation to optimize the bone regeneration capacity of gelatin-based cryogels

One of the key challenges in reconstructive bone surgery is to provide living constructs that possess the ability to integrate in the surrounding host tissue. Bone graft substitutes and biomaterials have already been widely used to heal critical-size bone defects due to trauma, tumor resection and tissue degeneration. In the present study, gelatin-based cryogels have been seeded with human SAOS-2 osteoblasts followed by the in vitro culture of the cells. In order to overcome the drawbacks associated with static culture systems, including limited diffusion and inhomogeneous cell-matrix distribution, the present work describes the application of a bioreactor to physically enhance the cell culture in vitro using an electromagnetic stimulus. The results indicate that the physical stimulation of cell-seeded gelatin-based cryogels upregulates the bone matrix production. We anticipate that the scaffolds developed consisting of human bone proteins and cells could be applied for clinical purposes related to bone repair.

Smart polymer hydrogels: properties, synthesis and applications

Abstract: Smart hydrogel systems with various chemically and structurally responsive moieties exhibit responsiveness to external stimuli including temperature, pH, ionic concentration, light, magnetic fields, electrical fields and chemicals. Polymers with multiple responsive properties have also been developed elegantly combining two or more stimuli-responsive mechanisms. Smart polymer hydrogels change their structural and volume phase transition as a response to external stimuli resulting in an enormous potential for scientific observations and for various advanced technological applications. This chapter will emphasize the most recent advances in the field. Further, developments of different smart hydrogels including their preparation and biomedical applications will be discussed in depth.

Synergistic effect of κ-carrageenan and gelatin blends towards adipose tissue engineering

The current paper focuses on the functionalization of κ-carrageenan and gelatin as extracellular matrix polysaccharide and protein mimic respectively to produce hydrogel films for adipose tissue engineering. More specifically, κ-carrageenan as well as gelatin have been functionalized with methacrylate and methacrylamide moieties respectively to enable subsequent UV-induced crosslinking in the presence of a photo-initiator. The gel fraction, the mass swelling ratio and the mechanical properties of both the one-component hydrogels and the protein/polysaccharide blends have been evaluated. The mechanical and swelling properties of the blends could be tuned by varying the hydrogel composition as well as the crosslinking method applied. The in vitro biocompatibility assays indicated a significantly higher cell viability of adipose tissue-derived mesenchymal stem cells seeded onto the blends as compared to the one-component hydrogels. The results show that the blends of gelatin and κ-carrageenan clearly outperform the one-component hydrogels in terms of adipose tissue engineering potential.

Plasma polymerisation of siloxanes at atmospheric pressure

Abstract This work deals with the plasma polymerisation of two siloxane precursors, [hexamethyldisiloxane (HMDSO) and tetramethyldisiloxane (TMDSO)] with an atmospheric pressure pseudoglow dielectric barrier discharge operated in argon and an argon–air mixture. The influence of gas composition and precursor type on the physical and chemical properties of the deposited films is examined in detail using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Results clearly show that precursor type as well as gas composition has an profound impact on film growth rate and chemical composition of the deposited films. Plasma polymerisation of both siloxane precursors in argon leads to the formation of hydrophobic polymers consisting of a Si–O–Si backbone, while for deposition in an argon–air mixture, hydrophilic inorganic silica-like coatings are obtained.